1. Field of the Invention
The present invention relates to novel and efficient vent covers for preventing the entry of moisture into so-called crawlspaces of buildings such as homes. Moisture is very damaging to wood structural support members of buildings and is absorbed by such members from the ground and from moist air in contact therewith.
Many buildings and homes are built without basements, and are elevated a few feet above the ground on support members such as stone, poured concrete or concrete block walls. In many cases the crawlspace between the ground surface and the wooden floor beams or joists of the house is at a level below the level of the surrounding soil, or below the level of saturated soils in wet weather, so that water flows into and is absorbed up through the floor of the crawlspace, usually a dirt surface, from adjacent ground areas of higher elevation and up from the sub-soil. Such water is drawn into the headroom of the crawl space in the form of water vapor and penetrates the wooden structural members of the building, causing wood rot, mold, odors, attraction of ants and other insects, rodents etc. Also, the escape of dangerous radon gas from the ground into the crawlspace and into the building is another problem.
Even in crawlspaces that do not leak or flood from groundwater, the earth below the crawlspace, and forming the floor of the crawlspace, has a high humidity level most of the time, and this water vapor rises into the crawlspace to produce a humid air atmosphere within the crawlspace, which moves upwardly to penetrate the structural framing and living spaces above the crawlspace.
Mold spores exist in air and grow into destructive mold in the presence of damp organic material, such as moist wood. Humidity levels of from 50% to 90% are common in crawlspaces, even those that have never flooded. Mold can grow on dirt, insulation, wood framing and even under carpeting on the floor within the home. Mold digests and destroys organic materials as it feeds on them. Damp environments also provide an inviting environment for insects such as termites, ants and similar critters which feed on moist organic material such as structural support wood and can contribute to the destruction and collapse thereof.
2. State of the Art
In an effort to prevent the penetration of water and water vapor into building crawlspaces it has been proposed to apply a continuous moisture barrier layer such as a thick plastic film over the dirt floor of the crawlspace. This has been proven to be unsatisfactory, per se, since water is drawn up from the ground, beneath the barrier, and leaks and/or vaporizes around the edges of the barrier into the crawlspace environment. Also, water vapor penetrates the walls of the crawlspace and/or otherwise enters the crawlspace and accumulates on top of the vapor barrier film and generates moisture which permeates into the wooden structural supports of the building resulting in rot and decay, mold and fungus, odors and vermin.
U.S. Pat. No. 5,642,967 discloses a system in which the barrier film is associated with an excavated pit filled with aggregate.
Water entering the crawlspace collects in the pit and is pumped from a sump when necessary. A vapor barrier film is applied over the dirt floor of the crawlspace, and over the pit and sump areas, to prevent moisture from entering the building. Such a system is unsatisfactory because it has no means for preventing the entry of ground water or water vapor and its accumulation on the surface of the barrier film, with the disadvantages discussed supra.
U.S. Pat. No. 6,575,666 discloses a system for waterproofing a crawlspace against the entry of sub-soil water vapor and also against the entry of external ground water and water vapor through the crawlspace walls to completely isolate the building from water vapor from the earth. The system of U.S. Pat. No. 6,575,666 comprises applying over the floor of the crawlspace, generally a dirt floor but sometimes a poured concrete floor, a continuous sealed plastic film barrier layer, and extending the barrier film vertically-upwardly to the tops of the walls to cover and seal the interior peripheral walls enclosing the crawlspace. This encapsulates the entire crawlspace against the penetration of external ground water or flood water, sub-soil water and water vapor onto the surface of the plastic barrier film and into the crawlspace atmosphere. According to U.S. Pat. No. 5,642,967, and in most crawlspace enclosures, the walls enclosing the crawlspace are provided with air-circulation vents which permit the entry of exterior air into the crawlspace to displace the humid atmosphere therewithin. In some cases the vents are temperature-controlled to open automatically when the exterior temperature is about 70° F. and to close gradually as the temperature drops to about 40° F. However, it has been found that air-circulation vents are unnecessary and disadvantageous in crawlspace enclosures, particularly those which have been waterproofed and moistureproofed, such as according to U.S. Pat. No. 6,575,666. This is because such vents let cold air enter in the winter and thus waste energy, and let hot humid air enter in the summer, which is cooled in the crawlspace and causes condensation, which makes the moisture problem in the crawlspace worse, not better. The manual or automatic closure vent vanes are ineffective for sealing the vents against the entry of moist air, thereby representing a breach of the encapsulation system. Removal of the vents and replacement with 8″×16″ cement blocks is difficult and time-consuming. Therefore there is a need for a means for sealing vents in the walls of a crawlspace enclosure to prevent the entry of unconditioned exterior air into the crawlspace, particularly in the case of otherwise encapsulated or sealed crawlspaces.